Electrochemical cells generally include an anode electrode and a cathode electrode separated by an electrolyte, where a proton exchange membrane (hereafter “PEM”) is used as the electrolyte. A metal catalyst and electrolyte mixture is generally used to form the anode and cathode electrodes. A well-known use of electrochemical cells is in a stack for a fuel cell (a cell that converts fuel and oxidants to electrical energy). In such a cell, a reactant or reducing fluid such as hydrogen is supplied to the anode, and an oxidant such as oxygen or air is supplied to the cathode. The hydrogen electrochemically reacts at a surface of the anode to produce hydrogen ions and electrons. The electrons are conducted to an external load circuit and then returned to the cathode, while hydrogen ions transfer through the electrolyte to the cathode, where they react with the oxidant and electrons to produce water and release thermal energy. An individual fuel cell consists of a number of functional components aligned in layers as follows: conductive plate/gas diffusion backing/anode electrode/membrane/cathode electrode/gas diffusion backing/conductive plate. Another well know use of PEM cells is in electrolysis of water to form hydrogen at the cathode and oxygen at the anode.
Long term stability of the proton exchange membrane is critically important for several industrial applications, such as fuels cells. For example, the lifetime goal for stationary fuel cell applications is 40,000 hours of operation. Typical membranes found in use throughout the art will degrade over time through decomposition of the fluoropolymer, accompanied by emission of fluoride ions and membrane thinning, thereby compromising membrane viability and performance. While not wishing to be bound by theory, it is believed that this degradation is a result of the reaction of the membrane fluoropolymer with radicals arising from the decomposition of hydrogen peroxide (H2O2) , which are generated during fuel cell operation.
Thus, it is desirable to develop a process for reducing or preventing proton exchange membrane degradation due to the membrane's interaction with hydrogen peroxide radicals, thereby sustaining its level of performance while remaining stable and viable for longer periods of time, wherein as a result, fuel cell costs can be reduced.
G.B. Patent No. 1,210,794 discloses that it is possible to increase the stability of fluoropolymers by reacting the unstable end groups and other unstable groups with fluorine radicals to form more chemically stable groups.
Several references have shown that incorporating inorganic fillers into fluoropolymers can improve many properties (Alberti et al., Solid State Ionics, 2001, 145: 249-255; U.S. Pat. No. 5,919,583).
There is still a need to further improve the stability of fluoropolymer membranes by a greater degree than has been achieved by existing treatment.